Providing resiliency to a raid group of storage devices

Abstract

A technique is directed to providing resiliency to a redundant array of independent disk (RAID) group which includes multiple storage devices. The technique involves operating the RAID group in a normal state in which each storage device is (i) initially online to perform write and read operations and (ii) configured to go offline in response to a respective media error count for that storage device reaching an initial take-offline threshold. The technique further involves receiving a notification that a storage device of the RAID group has encountered a particular error situation. The technique further involves transitioning, in response to the notification, the RAID group to a high resiliency state in which each storage device that is operable is (i) still online to perform write and read operations and (ii) configured to stay online even when the respective media error count for that storage device reaches the initial take-offline threshold.

What is claimed is: 
     
       1. A computer-implemented method of providing resiliency to a redundant array of independent disk (RAID) group which includes a plurality of storage devices, the method comprising:
 operating the RAID group in a normal state in which each storage device is (i) initially online to perform write and read operations and (ii) configured to go offline in response to a respective media error count for that storage device reaching an initial take-offline threshold; 
 receiving a notification that a storage device of the RAID group has encountered a particular error situation; and 
 in response to the notification, transitioning the RAID group from the normal state to a high resiliency degraded state in which each storage device that is operable is (i) still online to perform write and read operations and (ii) configured to stay online even when the respective media error count for that storage device reaches the initial take-offline threshold; 
 wherein receiving the notification includes electronically detecting that a first storage device of the RAID group has gone offline in response to the media error count for the first storage device reaching the initial take-offline threshold; and 
 wherein transitioning includes electronically preventing a second storage device of the RAID group from going offline in response to the media error count for the second storage device reaching the initial take-offline threshold, 
 the RAID group thereby made to operate in the high resiliency degraded state in which the second storage device remains online performing write and read operations even though the media error count of the second storage device has reached the initial take-offline threshold. 
 
     
     
       2. A computer-implemented method as in  claim 1  wherein preventing includes:
 configuring the second storage device to remain online regardless of a respective media error count for the second storage device. 
 
     
     
       3. A computer-implemented method as in  claim 2  wherein electronically detecting includes:
 receiving, as the notification, an alert indicating that the first storage device has gone offline in response to a respective media error count for the first storage device reaching the initial take-offline threshold. 
 
     
     
       4. A computer-implemented method as in  claim 2 , further comprising:
 receiving an alert indicating that a proactive copy operation has begun in response to an accounting for the first storage device reaching an end-of-life threshold, the proactive copy operation involving proactively copying data from the first storage device of the RAID group to a spare storage device. 
 
     
     
       5. A computer-implemented method as in  claim 4 , further comprising:
 proactively copying data from the first storage device of the RAID group to the spare storage device while all of the storage devices of the RAID group remain online to perform write and read operations. 
 
     
     
       6. A computer-implemented method as in  claim 4 , further comprising:
 reconstructing data that was not proactively copied from the first storage device of the RAID group to the spare storage device, and storing that reconstructed data on the spare storage device. 
 
     
     
       7. A computer-implemented method as in  claim 2  wherein processing circuitry maintains a hierarchy of objects representing the RAID group; and wherein electronically detecting includes:
 obtaining, by a RAID group object of the hierarchy, an alert indicating existence of the particular error situation, the RAID group object representing the RAID group. 
 
     
     
       8. A computer-implemented method as in  claim 7  wherein electronically preventing includes:
 providing a respective don't-take-offline command from the RAID group object of the hierarchy to a storage device object of the hierarchy, the storage device object of the hierarchy representing the second storage device of the RAID group. 
 
     
     
       9. A computer-implemented method as in  claim 1  wherein preventing the second storage device of the RAID group from going offline includes:
 sending, from processing circuitry and to the second storage device, a command that disables the second storage device from going offline in response to the media error count for the second storage device reaching the initial take-offline threshold. 
 
     
     
       10. A computer program product having a non-transitory computer readable medium which stores a set of instructions to provide resiliency to a redundant array of independent disk (RAID) group which includes a plurality of storage devices, the set of instructions, when carried out by computerized circuitry, causing the computerized circuitry to perform a method of:
 operating the RAID group in a normal state in which each storage device is (i) initially online to perform write and read operations and (ii) configured to go offline in response to a respective media error count for that storage device reaching an initial take-offline threshold; 
 receiving a notification that a storage device of the RAID group has encountered a particular error situation; and 
 in response to the notification, transitioning the RAID group from the normal state to a high resiliency degraded state in which each storage device that is operable is (i) still online to perform write and read operations and (ii) configured to stay online even when the respective media error count for that storage device reaches the initial take-offline threshold; 
 wherein receiving the notification includes electronically detecting that a first storage device of the RAID group has gone offline in response to the media error count for the first storage device reaching the initial take-offline threshold; and 
 wherein transitioning includes electronically preventing a second storage device of the RAID group from going offline in response to the media error count for the second storage device reaching the initial take-offline threshold, 
 the RAID group thereby made to operate in the high resiliency degraded state in which the second storage device remains online performing write and read operations even though the media error count of the second storage device has reached the initial take-offline threshold. 
 
     
     
       11. A computer program product as in  claim 10  wherein electronically preventing includes:
 configuring the second storage device to remain online regardless of a respective media error count for the second storage device. 
 
     
     
       12. A computer program product as in  claim 11  wherein electronically detecting includes:
 receiving, as the notification, an alert indicating that the first storage device has gone offline in response to a respective media error count for the first storage device reaching the initial take-offline threshold. 
 
     
     
       13. A computer program product as in  claim 11 , further comprising:
 receiving an alert indicating that a proactive copy operation has begun in response to an accounting for the first storage device reaching an end-of-life threshold, the proactive copy operation involving proactively copying data from the first storage device of the RAID group to a spare storage device. 
 
     
     
       14. A computer program product as in  claim 11  wherein processing circuitry maintains a hierarchy of objects representing the RAID group; and wherein electronically detecting includes:
 obtaining, by a RAID group object of the hierarchy, an alert indicating existence of the particular error situation, the RAID group object representing the RAID group. 
 
     
     
       15. A computer program product as in  claim 14  wherein electronically preventing includes:
 providing a respective don't-take-offline command from the RAID group object of the hierarchy to a storage device object of the hierarchy, the storage device object of the hierarchy representing the second storage device of the RAID group. 
 
     
     
       16. A computer program product as in  claim 10  wherein preventing the second storage device of the RAID group from going offline includes:
 sending, from the computerized circuitry and to the second storage device, a command that disables the second storage device from going offline in response to the media error count for the second storage device reaching the initial take-offline threshold. 
 
     
     
       17. Data storage equipment, comprising:
 a set of host interfaces to interface with a set of host computers; 
 a redundant array of independent disk (RAID) group which includes a plurality of storage devices to store host data on behalf of the set of host computers; and 
 control circuitry coupled to the set of host interfaces and the RAID group, the control circuitry being constructed and arranged to:
 operate the RAID group in a normal state in which each storage device is (i) initially online to perform write and read operations and (ii) configured to go offline in response to a respective media error count for that storage device reaching an initial take-offline threshold, 
 receive a notification that a storage device of the RAID group has encountered a particular error situation, and 
 in response to the notification, transition the RAID group from the normal state to a high resiliency degraded state in which each storage device that is operable is (i) still online to perform write and read operations and (ii) configured to stay online even when the respective media error count for that storage device reaches the initial take-offline threshold; 
 
 wherein receiving the notification includes electronically detecting that a first storage device of the RAID group has gone offline in response to the media error count for the first storage device reaching the initial take-offline threshold; and 
 wherein transitioning includes electronically preventing a second storage device of the RAID group from going offline in response to the media error count for the second storage device reaching the initial take-offline threshold, 
 the RAID group thereby configured to operate in the high resiliency degraded state in which the second storage device remains online to perform write and read operations even though the media error count of the second storage device has reached the initial take-offline threshold. 
 
     
     
       18. Data storage equipment as in  claim 17  wherein the control circuitry, when electronically preventing, is constructed and arranged to:
 configure the second storage device to remain online regardless of the respective media error count for the second storage device. 
 
     
     
       19. Data storage equipment as in  claim 18  wherein the control circuitry, when electronically detecting, is constructed and arranged to:
 receive an alert indicating that the first storage device has gone offline in response to a respective media error count for the first storage device reaching the initial take-offline threshold. 
 
     
     
       20. Data storage equipment as in  claim 18  wherein the control circuitry is further constructed and arranged to:
 receive an alert indicating that a proactive copy operation has begun in response to an accounting for the first storage device reaching an end-of-life threshold, the proactive copy operation involving proactively copying data from the first storage device of the RAID group to a spare storage device. 
 
     
     
       21. Data storage equipment as in  claim 18  wherein the control circuitry maintains a hierarchy of objects representing the RAID group; and wherein the control circuitry, when electronically detecting, is constructed and arranged to:
 obtain, by a RAID group object of the hierarchy, an alert indicating existence of the particular error situation, the RAID group object representing the RAID group. 
 
     
     
       22. Data storage equipment as in  claim 21  wherein the control circuitry, when electronically preventing, is constructed and arranged to:
 provide a respective don't-take-offline command from the RAID group object of the hierarchy to a storage device object of the hierarchy, the storage device object of the hierarchy representing the second storage device of the RAID group. 
 
     
     
       23. Data storage equipment as in  claim 17  wherein preventing the second storage device of the RAID group from going offline includes:
 sending, from the control circuitry and to the second storage device, a command that disables the second storage device from going offline in response to the media error count for the second storage device reaching the initial take-offline threshold.